In Japanese Published Unexamined Patent Application No. 2007-62147, an invention relating to a glue application apparatus that applies glue to the back edge face of a booklet structure made up of gathered sheets is disclosed. As described in that document, this glue application apparatus includes a container 6 storing glue for binding, a drum 7 that is installed inside the container 6 and rotates with its surface covered by glue, and clampers 4 that nip a booklet structure between them and can reciprocate and pass above the drum 7. According to this apparatus, as the clampers 4 that clamp a booklet structure pass above the rotating drum 7, the back edge face of the booklet structure is brought into contact with the drum 7; as a result, glue can be applied to the back edge face of the booklet structure nipped between the clampers 4. In this apparatus, a motor 8 that drives and rotates the drum 7 and a motor 9 that drives and moves the clampers 4 are provided separately. It is set forth that, by arbitrarily setting the rotating speeds of the respective motors 8 and 9, it is possible to arbitrarily change a relative speed between the circumferential speed of the drum 7 and the passage speed of the clampers 4 and properly perform glue application to the back edge face of the booklet structure. In the foregoing description, the reference numerals of the respective components are as found in the patent document listed below.
Japanese Published Unexamined Patent Application No. 2007-62147.
According to the present invention, titled “glue application apparatus”, described in Japanese Published Unexamined Patent Application No. 2007-62147, applying a glue onto the back edge face of a booklet structure is performed by making the booklet structure pass above the drum once, while bringing its back edge face into contact with the rotating drum. Explaining this with reference to FIGS. 10A to 10C, when the drum 100 is made to rotate in a direction indicated by arrow A in FIG. 10A, a single action of moving the booklet structure 101 to the right hand in the figure is performed, while bringing the back edge face 102 of the booklet structure 101 into contact with the top of the drum 100, thus applying the glue G onto the back edge face 102. However, according to such a glue application method, in practice, there is a problem in which it may sometimes be impossible to apply the glue G with a proper thickness evenly onto the back edge face 102 of the booklet structure 101.
In applying the glue G using the drum 100 in this way, the quantity of the glue G to be applied onto the back edge face 102 of the booklet structure 101 is generally proportional to the thickness of the booklet structure 101. Also, the quantity of the glue G that is applied onto the back edge face 102 of the booklet structure 101 is determined by an amount of rotation (rotation angle) of the drum 100. Hence, if the thickness of the booklet structure 101 is large, the amount of rotation of the drum 100 must be increased accordingly to apply a required quantity of glue G onto the back edge face 102. In some cases, however, it is found to make it impossible to apply the glue G in more than a given quantity onto the back edge face 102, because the glue G drawn from the container and adhered to the drum 100 is fed to between the back edge face 102 and the drum 100 which are in contact with each other, but some of the glue G is blocked by the back edge face 102 and the drum 100 and pushed back. Even though it is attempted to feed a required quantity of the glue G, some of the fed glue G slips down along the circumferential surface of the drum 100 to upstream in the rotation direction, as indicated by arrow B in FIG. 10A.
Even if a lot of glue G has been made to adhere to the back edge face 102 in this way, a uniform distribution of the glue G over the back edge face 102 cannot be attained because of a single action of glue G application. Also, because a quantity of glue that can be kept adhered to the back edge face 102 against gravity is limited in view of viscosity of the glue G that is generally used, it occurs that a portion of the glue G adhered to the back edge face 102, especially a heavily adhered glue portion drops by the force of the gravity and the quantity of the glue G remaining on the back edge face 102 decreases, as illustrated in FIG. 10B. Therefore, in some cases, it is found that the quantity of the glue G that can be applied onto the back edge face 102 is not necessarily sufficient for good binding.
When the booklet structure 101 moves from left to right in FIG. 10, while contacting the drum 100, the glue G is applied to its back edge face 102. In this glue application method, it tends to be difficult to attain uniform distribution over the back edge face 102, as noted previously. That is, as illustrated in FIG. 10C, in an end position of the edge face (left in the figure) where glue G application begins, the quantity of the glue G that adheres to the back edge face 102 is less, as noted previously, whereas, in an end portion of the edge face (right in the figure) where the back edge face 102 of the booklet structure 101 is away from the drum 100, the fed glue G is liable to remain on the back edge face 102, thus resulting in a larger quantity of the glue G adhered to the face. As a result, it is found that some of the glue G drops, as noted previously, which makes the quantity of the glue G adhered to the back edge face 102 insufficient, and the condition of adhesion of the glue G over the back edge face 102 becomes uneven.
Therefore, in bookbinding through the use of the foregoing glue application apparatus of related art, it is difficult to apply a required quantity of an adhesive agent evenly over the back edge face of a bundle of text sheets into which plural text sheets have been gathered. In consequence, it has been impossible to avoid the occurrence of troubles such as spine split meaning that a finished book (booklet) is split intermediately along its thickness direction and loose sheets meaning that some of text sheets are loosen off from a bundle of text sheets.
The prevent invention has been made in the light of the foregoing problem and is intended to provide a bookbinding apparatus that is capable of applying an adhesive agent with a suitable thickness evenly over the back edge face of a bundle of text sheets, thus reducing the likelihood of occurrence of troubles such as spine split and loose sheets in a finished book.